The present invention relates to a measurement arrangement for detecting the gas charge of a plastic component.
In foam systems as described herein, it is known that an A-component (e.g., polyol) is kept under controlled pressure in a component container. A second component (the B-component), which has a circuit identical to that described below for the A-component, is present. The two components are introduced together into a mixer head and then applied to a workpiece by injection through an injection head, whereby the air contained in the A-component is the determining factor for the porosity of the injection molded plastic article. It is also possible that the B-component may unintentionally contain air which can then also have an effect on the foam.
Such a plastic article is preferably a seal, which is sprayed with the abovementioned system onto a workpiece and then reacts chemically, whereby the seal foams and then hardens.
Until now, there existed the problem that the air portion in the A-component could be kept uniform only with difficulty, since until now it was known to blow this air into the A-component container, mixing it as intimately as possible with this A-component through the action of a stirring device.
Since the interior of the component container is under pressure and the air is introduced into the A-component in fine beads under higher pressure, the air bonds to the A-component. This A-component mixture combined with air is fed to the mixing head via a material outlet and a dosing pump.
It is also known to provide the B-component with an identical circuit, consisting of a component container, material outlet, dosing pump, and inlet into the mixing head, with no air added to the B-component, although it may contain air.
As already mentioned, it was, until now, difficult to regulate the amount of air in the component container such that a uniform percentage of air was always maintained in the A-component regardless of the fullness of the component container.
It has previously been known to detect the amount of air in the A-component by means of a measuring arrangement disposed in the outlet of the A-component container.
The measuring principle of this measuring arrangement was based on the fact that the liquid to be measured was introduced into a measuring chamber, in which measuring chamber a sound generator and sound receiver were present. By bombarding the volume to be measured with sound, a certain attenuation of the sound waves was generated due to the air contained in the A-component, which attenuation was detected by the sound receiver. By evaluating the attenuation, it was possible to determine the proportion of air in the A-component. However, a disadvantage of the known measuring arrangement is that the cost of measurement is unreasonably high and such a device is very expensive to produce and to service.
The object of the present invention is therefore to improve a measurement arrangement of the type mentioned in the introduction such that it is significantly more cost-effective to produce, operates more reliably, and assures fast monitoring of the air contained in the A-component.